ArrayList和LinkedList的區別是什么？

• ArrayList基於動態數組實現的非線程安全的集合；LinkedList基於鏈表實現的非線程安全的集合。
• 對於隨機index訪問的get和set方法，一般ArrayList的速度要優於LinkedList。因為ArrayList直接通過數組下標直接找到元素；LinkedList要移動指針遍歷每個元素直到找到為止。
• 新增和刪除元素，一般LinkedList的速度要優於ArrayList。因為ArrayList在新增和刪除元素時，可能擴容和復制數組；LinkedList實例化對象需要時間外，只需要修改指針即可。
• LinkedList集合不支持 高效的隨機隨機訪問（RandomAccess）
• ArrayList的空間浪費主要體現在在list列表的結尾預留一定的容量空間，而LinkedList的空間花費則體現在它的每一個元素都需要消耗相當的空間

 

測試代碼

public static void main(String[] args) {
        ArrayList<Integer> arrayList = new ArrayList<Integer>();
        LinkedList<Integer> linkedList = new LinkedList<Integer>();
        int size = 10000 * 1000;
        int index = 5000 * 1000;
        
        System.out.println("arrayList add " + size);
        addData(arrayList, size);
        System.out.println("linkedList add " +  + size);
        addData(linkedList, size);
        System.out.println();
        
        System.out.println("arrayList get " + index + " th");
        getIndex(arrayList, index);
        System.out.println("linkedList get " + index + " th");
        getIndex(linkedList, index);
        System.out.println();
        
        System.out.println("arrayList set " + index + " th");
        setIndex(arrayList, index);
        System.out.println("linkedList set " + index + " th");
        setIndex(linkedList, index);
        System.out.println();
        
        System.out.println("arrayList add " + index + " th");
        addIndex(arrayList, index);
        System.out.println("linkedList add " + index + " th");
        addIndex(linkedList, index);
        System.out.println();
        
        System.out.println("arrayList remove " + index + " th");
        removeIndex(arrayList, index);
        System.out.println("linkedList remove " + index + " th");
        removeIndex(linkedList, index);
        System.out.println();
        
        System.out.println("arrayList remove Object " + index);
        removeObject(arrayList, (Object)index);
        System.out.println("linkedList remove Object " + index);
        removeObject(linkedList, (Object)index);
        System.out.println();
        
        System.out.println("arrayList add");
        add(arrayList);
        System.out.println("linkedList add");
        add(linkedList);
        System.out.println();
        
        System.out.println("arrayList foreach");
        foreach(arrayList);
        System.out.println("linkedList foreach");
        foreach(linkedList);
        System.out.println();
        
        System.out.println("arrayList forSize");
        forSize(arrayList);
        System.out.println("linkedList forSize");
//        forSize(linkedList);
        System.out.println("cost time: ...");
        System.out.println();
        
        System.out.println("arrayList iterator");
        ite(arrayList);
        System.out.println("linkedList iterator");
        ite(linkedList);
    }
    
    private static void addData(List<Integer> list, int size) {
        long s1 = System.currentTimeMillis();
        for (int i = 0; i <size; i++) {
            list.add(i);
        }
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void getIndex(List<Integer> list, int index) {
        long s1 = System.currentTimeMillis();
        list.get(index);
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void setIndex(List<Integer> list, int index) {
        long s1 = System.currentTimeMillis();
        list.set(index, 1024);
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void addIndex(List<Integer> list, int index) {
        long s1 = System.currentTimeMillis();
        list.add(index, 1024);
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void removeIndex(List<Integer> list, int index) {
        long s1 = System.currentTimeMillis();
        list.remove(index);
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void removeObject(List<Integer> list, Object obj) {
        long s1 = System.currentTimeMillis();
        list.remove(obj);
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void add(List<Integer> list) {
        long s1 = System.currentTimeMillis();
        list.add(1024);
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void foreach(List<Integer> list) {
        long s1 = System.currentTimeMillis();
        for (Integer i : list) {
            //do nothing
        }
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void forSize(List<Integer> list) {
        long s1 = System.currentTimeMillis();
        int size = list.size();
        for (int i = 0; i <size; i++) {
            list.get(i);
        }
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }
    
    private static void ite(List<Integer> list) {
        long s1 = System.currentTimeMillis();
        Iterator<Integer> ite = list.iterator();
        while (ite.hasNext()) {
            ite.next();
        }
        long s2 = System.currentTimeMillis();
        System.out.println("cost time: " + (s2-s1));
    }

 

 

JDK1.8，win7 64位。結果

arrayList add 10000000
cost time: 3309
linkedList add 10000000
cost time: 1375
 
arrayList get 5000000 th
cost time: 0
linkedList get 5000000 th
cost time: 53
 
arrayList set 5000000 th
cost time: 0
linkedList set 5000000 th
cost time: 44
 
arrayList add 5000000 th
cost time: 3
linkedList add 5000000 th
cost time: 45
 
arrayList remove 5000000 th
cost time: 3
linkedList remove 5000000 th
cost time: 46
 
arrayList remove Object 5000000
cost time: 31
linkedList remove Object 5000000
cost time: 131
 
arrayList add
cost time: 0
linkedList add
cost time: 0
 
arrayList foreach
cost time: 30
linkedList foreach
cost time: 128
 
arrayList forSize
cost time: 5
linkedList forSize
cost time: ...
 
arrayList iterator
cost time: 6
linkedList iterator
cost time: 113

 

 

思考：

• arrayList add 10000000 cost time: 3293；linkedList add 10000000 cost time: 1337
• arrayList add 1000000  cost time: 22  ；   linkedList add 1000000   cost time: 1011
• 跑另外一組數據，size設為1000 * 1000，得出當size增加，ArrayList的add操作的累計時間增長更快
• 千萬別在循環中調用LinkedList的get方法，耗時會讓你崩潰
• 代碼例子中，"新增和刪除元素，一般LinkedList的速度要優於ArrayList"並不成立，可以思考一下原因。
   

源碼分析參考：

• https://blog.csdn.net/luyuqin0115/article/details/80395694

   

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